1. Field of the Invention
This invention relates to a control apparatus and method for a transmission mechanism for a vehicle provided with the transmission, and a method of estimating the heat value of an electric motor.
2. Description of Related Art
An electronically, continuously variable transmission (ECVT) is known in which a transmission ratio may be changed continuously using an electric motor (see JP-A-2004-19740, for example.).
In an ECVT, the electric motor is driven in reverse relatively often due to changes in transmission ratio. As a result, a relatively large amount of heat is generated, leading to temperature rise in the electric motor and its driving circuit, and to the possibility of deterioration in motor performance.
Therefore, the motor temperature or heat value is preferably monitored so that the motor temperature does not exceed a permissible use temperature range. For example, a method of estimating the motor temperature is conceivable in which temperature sensors are provided on the motor, its driving circuit etc. Because the heat value of the motor is in proportion to the square of the current flowing through the motor, another conceivable method is to provide a current sensor to measure the current flowing through the motor, and estimate the heat value from the measured current.
The methods mentioned above, however, require separate temperature and current sensors to be provided. As a result, constitution and control of the ECVT is undesirably complicated.